Recently, lithium secondary batteries used as main electrical sources for mobile communicating appliances, portable electrical appliances and the like have high potential force and energy density.
A carbon material capable of absorbing and desorbing lithium ions has been used as the negative electrode material of the lithium secondary battery. However, the theoretical capacity of graphite, which is one of the carbon materials, is 372 mAh/g and this is only about 10% of theoretical capacity of elemental metallic lithium. In order to further increase the capacity of the lithium secondary battery, therefore, it is essential to develop novel types of negative electrode materials.
From this viewpoint, for example, Japanese Laid-open patent publication No. Hei 7-240201 has proposed a silicate of non-iron metal as a negative electrode material, while Japanese Laid-open patent publication No. Hei 9-63651 has proposed a negative electrode material which is composed of an intermetallic compound comprising a 4B Group element and at least one of P and Sb and has a crystal structure of CaF2 type, ZnS type or AlLiSi type.
Japanese Laid-open patent publication No. Hei 11-86854 has proposed a negative electrode material comprising particles which include a phase composed of Si, Sn or the like and a phase composed of an intermetallic compound whose constituent elements are Si, Sn and the like.
However, the electron conductivity of the alloy material containing at least Si or Sn as thus described is not very high. When this alloy material is used for the electrode, therefore, a conductive material should also be used for the purpose of enhancing the electron conductivity in the electrode.
There is also a problem that a volume change of the alloy material containing at least Si or Sn at the time of absorbing and desorbing lithium is relatively larger than that of the carbon material or the like. Namely, an alloy powder used for the negative electrode of the lithium secondary battery is destroyed through the repetition of charge/discharge to be more finely divided. Occurrence of the fine division causes generation of particles that cannot be involved in an electrochemical reaction, leading to deterioration of the electron conductivity as a whole.
Accordingly, it is an object of the present invention to provide a negative electrode for a non-aqueous electrolyte secondary battery having an improved charge/discharge cycle characteristic by using an alloy containing at least silicon or tin as a constituent element for the negative electrode and improving the electron conductivity of the negative electrode thereof, thereby solving the aforesaid problems.